1. Field of Invention
This invention relates to the art of combustion of fuels and specifically to methods and apparatuses for optimizing the flow of air and fuel to the combustion apparatus to maximize combustion efficiency.
More specifically, this invention relates to simple combustion control systems employing mechanical linkage, or one specific unaltered signal, to position the fuel and air control devices to achieve the desired rate of energy release and also provide a means of maintaining the desired fuel to air ratio at all times despite variations in the qualities of the fuel or air. These variations can be caused by changes in density, moisture content, BTU value and the like, and by the method of this invention effectively overcoming the time lag existing between the formation of the fuel and air mixture and the analysis of exhaust gases.
2. Description of the Related Art
It is known in the art to adjust the combination of air and fuel being supplied to the combustion chamber to maximize the combustion efficiency. It is also known in the art to accomplish this through means of a mechanical linkage control. It is also known in the art to analyze the exhaust gases of the combustion process in order to determine whether or not proper combustion is taking place and what adjustments need to be made. It is also known in the art to provide a signal from an exhaust gas analyzer to drive different control mechanisms, such as valves and dampers.
When fuel is combusted with air, the flow of air and fuel must be controlled in a chemically correct relationship to achieve the most efficient combustion. A common way of achieving the desired air flow and fuel relationship is to interconnect the air flow regulating devices with the fuel control devices by means of mechanical linkages or control signals in a pre-calibrated manner. The mechanical linkages or control signals are pre-calibrated so that, as the rate of combustion is increased or decreased in response to the energy release requirements of the end user, the air and fuel control devices operate in a manner that provides the desired relationship between fuel flow and air flow regardless of the rate of combustion or energy release requirement of the combustion apparatus.
One disadvantage of the above-described system is that it is unresponsive to day-to-day variations in the atmosphere, fuel, and other factors which can affect the combustion equation. For example, variations in fuel qualities, and ambient temperatures, and moisture content of the combustion air, and the like can alter the chemical correctness of the pre-calibrated relationship between air flow and fuel flow. In such cases, the combustion process operates less efficiently.
The above-described changes to the desired chemical relationship between air flow and fuel flow are commonly detected by sensors which monitor the exhaust gases of the combustion chamber. The sensors can detect the amount of residual, unburned oxygen and/or the amounts of carbon monoxide, carbon dioxide, or other substances in the products of combustion which exit the combustion chamber with the exhaust gases. Such detecting devices have been used in connection with various control devices to correct for the variations affecting the desired air flow to fuel flow chemistry. Most of these systems suffer from a relatively high installed cost and are complex. Further, many have inadequate performance and require specialized maintenance and the like.
To avoid the complexity and high installed cost of the prior art devices, this invention provides a relatively simple means of compensating for the effect of temperature and similar variations on the desired chemically correct pre-calibrated relationship between air flow and fuel flow. The invention enables the pre-calibrated relationship between fuel flow and air flow to be compensated for differences by adding a second moveable element to one or more of the prior art flow control devices.
The prior art flow control devices work on the principle of an established known relationship between the position of a moveable element or interconnected moveable elements designed to increase or decrease port area within the device through which the fluid can pass. By increasing the port area within the device, the rate of fluid flow can be increased. This relationship is commonly known as the "flow characteristic" of the flow control device.
It is known that the molecular content of the fluid flowing through the device increases or decreases with variations in temperature, solution, mixture strength, and other variations in the fluid's quality. Consequently, when the control device is used in a pre-calibrated manner to deliver a desired chemically correct rate of flow, the flow characteristic of the flow control device must be altered to compensate for the effect of the temperature difference or other variation in fluid quality. This invention provides a means for such flow control device to also have the capability to compensate for variations in temperature, fluid qualities, etc. This invention correctly adjusts the pre-calibration between the rate of combustion air flow control device and the rate of fuel flow control device to compensate for uncontrolled variations in air or fuel quality so that at any and all air and fuel rates of flow the pre-calibrated relationship between the air and fuel control devices will be substantially correct before, during and after rate of flow changes. The method of this invention largely overcomes the detrimental effect of the time lag existing between the point of fuel and air mixture formation and the exhaust gas analysis relating to that specific mixture This invention further provides a fail safe mechanism which permits the combustion process to proceed safely without interruption should faults occur in the exhaust gas analyzer, controller, or motion generation means for positioning the compensating second moveable element.